The main thrust of the present work is the investigation of mechanisms operating in the activation of carotid body chemoreceptors. Several approaches have been followed: 1) a study of the generator potential in these receptors using in vitro preparations and air gap techniques; 2) intracellular studies of glomus type I cells which have showed that these cells have great sensitivity to temperature changes which is reflected in marked variations in membrane potential and input resistance. The cells also react vigorously to CO2 of pH changes. These phenomena are dependent to a large extent on the Cl and Na concentrations of the external medium; 3) slices prepared from frozen tissues and observed under Nomarski optics are amenable to direct investigation with microelectrodes: they survive and behave like normal specimens; 4) regeneration studias have shown that growing nerve fibers have to make contact with glomus calls in order to be functionally active. Thus, the glomus cells play an important role in the generation of impulses; 5) autoradiographic studies have shown that nerve endings apposing on glomus cells readily take radiolabeled materials injected into the petrosal ganglion. Thus, they are sensory and not efferent as postulated by others; 6) neurochemical studies have shown that glomus cells (type I and/or type II) have high affinity for radioactive choline, ACh is formed and released upon stimulation. This supports the previously proposed role of ACh in the generation of chemosensory impulses. It is proposed to continue these studies during the next year since they show promise of unraveling the mechanisms of chemosensory function. BIBLIOGRAPHIC REFERENCES: McQueen, D.S. and C. Eyzaguirre (1974). Effects of temperature on carotid chemoreceptor and baroreceptor activity. J. Neurophysiol., 37, No 6:1287-1296. Eyzaguirre, C., S. Fidone and K. Nishi (1975). Recent studies on the generation of chemoreceptor impulses. The Peripheral Arterial Chemoreceptors, ed. Purves, M.J. Cambridge University Press, pp 175-194.